1. Field of the Invention
The present invention relates to an organic electroluminescent device and a method of fabricating the same, and more particularly, to a dual panel type organic electroluminescent device and method for fabricating the same that include an array device having a thin film transistor and an organic electroluminescent diode element formed on different substrates.
2. Discussion of the Related Art
In general, an organic electroluminescent device (ELD), which is a type of flat panel display, emits light by injecting electrons from a cathode and holes from an anode into an emission layer, combining the electrons with the holes, generating an exciton, and transitioning the exciton from an excited state to a ground state. Unlike a liquid crystal display (LCD) device, an additional light source is not necessary for the organic ELD to emit light. Accordingly, the organic ELD has a light weight, thin profile, compact size, wide viewing angle, and high image contrast. In addition, the organic ELD can operate using a DC low voltage, thereby having low power consumption and fast response time. Further, the organic ELD is an integrated device and it has high endurance of external impacts and a wide range of applications. Moreover, since fabricating an organic ELD is a relatively simple process, an organic ELD has a low production cost.
FIG. 1 is a schematic view of a unit pixel area of an organic electroluminescent device according to the related art. In FIG. 1, a scan line is formed along a first direction. A signal line and a power supply line are formed along a second direction perpendicular to the first direction and crossing the scan line, thereby defining a pixel area. A switching thin film transistor (TFT) Ts serving as an addressing element is formed at a crossing point of the scan line and the signal line, and connects to a storage capacitance CST. The switching TFT Ts controls voltage, and the storage capacitance CST stores a current source.
In addition, a drive TFT TD serving as a current source element is connected between the switching TFT Ts and the storage capacitance CST. One terminal of the drive TFT TD is connected to the power supply line, and another terminal is connected to an anode (+) electrode. The anode electrode is connected with a cathode (−) electrode through an electroluminescent diode “E” operating in a static current driving method. The anode electrode and the cathode electrode connected by the electroluminescent diode “E” constitute an organic electroluminescent device.
As a signal is applied to a corresponding electrode according to a selection signal, the gate of the switching TFT Ts is turned on. Accordingly, a data signal passes through the gate of the switching TFT Ts and is applied to the drive TFT TD and the storage capacitance CST. As the gate of the drive TFT TD is turned on, a current is applied from the power supply line to the organic electroluminescent diode E through the gate of the drive TFT TD, thereby emitting light. In addition, since an open degree of the drive TFT TD is varied based on the data signal, a desired gray scale can be displayed by controlling amount of current flowing through the drive TFT TD. Further, during a non-selected period, data charged in the storage capacitance CST is continuously applied to the drive TFT TD, thereby allowing the organic electroluminescent device to emit light until a next image signal is applied.
FIGS. 2A to 2C are views illustrating an organic electroluminescent device according to the related art. Specifically, FIG. 2A is a plane view of a panel, FIG. 2B is a sectional view of the panel, and FIG. 2C is a sectional view taken along IIc—IIc of FIG. 2A.
As shown in FIG. 2A, a panel includes a substrate 10 having a first region IIa and a second region IIb enclosing the first region IIa. The first region IIa includes a first sub-region IIaa corresponding to an image display region, and a second sub-region IIab corresponding to a region between the image display region and a seal pattern. Although not shown, a plurality of gate lines, data lines, power supply lines and the like defining a plurality of pixel areas are formed within the first region IIa and an electroluminescent device is included in each of the pixel areas.
In addition, first, second, third and fourth array pads 20, 22, 24 and 26 are formed along four sides of the substrate 10. The first array pad 20 is a group of gate pads for applying a gate signal to the gate lines, the second array pad 22 is a group of data pads for applying a data signal to the data lines, the third array pad 24 is a group of power pads for applying a Vdd signal to the power supply lines, and the fourth array pad 26 is a ground pad to which a ground current is applied. Further, the fourth array pad 26 is a circle pattern and has a larger area than the first, second and third array pads, 20, 22, and 24, due to an electrical characteristic of a DC current applied to a common electrode array pad.
The first region IIa of the first substrate 10 is sealed by an encapsulation substrate 30 and is shielded from the exterior. The encapsulation substrate 30 is formed of a thin passivation film, a glass substrate, or a plastic substrate.
The sectional view of FIG. 2B is shown centering on the encapsulation structure, and omitting the pads. As shown in FIG. 2B, a seal pattern 32 for sealing the first region IIa of the first substrate 10 with the encapsulation substrate 30 is formed on a peripheral portion enclosing the first region IIa of the first substrate 10. The first region IIa includes a plurality of pixel areas “P” and TFTs “T” formed in the pixel areas “P.” The first region IIa also includes a first electrode 12 connecting to the TFTs “T.” The first electrode 12 includes a transparent electrode material. An organic electroluminescent layer 14 for emitting red (R), green (G) and blue (B) color lights is formed on the first electrode 12. A second electrode 16 is formed on an entire surface of the organic electroluminescent layer 14 and functions as a common electrode. The first and second electrodes 12 and 16, and the organic electroluminescent layer 14 interposed between the first and second electrodes 12 and 16 constitute an organic electroluminescent diode element “E,” such that the organic electroluminescent layer 14 emits light toward the first electrode 12.
In FIG. 2C, the second electrode 16 receives current applied through one of the array pads, 20, 22, 24 and 26 (shown in FIG. 2A). For example, the second electrode 16 electrically connects to the fourth array pad 26 in the second sub-region IIab. In other words, one end of the second electrode 16 extends from the first sub-region IIaa into the second sub-region IIab, and one end of the fourth array pad 26 extends from the second region IIb into the second sub-region IIab.
Accordingly, the organic electroluminescent device according to the related art is fabricated by forming the array device and the organic electroluminescent diode element on a substrate and attaching the substrate to the encapsulation substrate and fabrication yields of the array device and the organic electroluminescent diode element determine an overall yield of the organic electroluminescent device. Thus, even if the array device is formed without defects but the organic electroluminescent diode element is formed with a defect, e.g., foreign particles in the organic electroluminescent layer, the organic electroluminescent device panel would be defective, thereby reducing fabrication yield and increasing fabrication costs increases.
In addition, the above-described organic electroluminescent device is classified as a lower luminescent way because its luminescence depends on the transparency of the electrode. Although the lower luminescent way device has high stability and process freedom due to the encapsulation, it has a small aperture ratio, thereby limiting its application in high resolution products.
The upper luminescent way device has an easy design, enhanced aperture ratio, and longer life span. However, in the related art upper luminescent way, since a cathode is generally disposed on an organic electroluminescent layer, specific materials are required and light transmissivity is limited, thereby lowering light efficiency. Also, when a thin passivation film is formed to minimize the lowering of light transmissivity, the related art upper luminescent way fails to sufficiently block exterior air.